TOKYO (Reuters) - The mother of a Japanese journalist being held captive by Islamic State militants along with another Japanese citizen appealed for his safe release on Friday as a ransom deadline neared and the Japanese government raced to respond.

In an online video released on Tuesday, a black-clad figure holding a knife stood between journalist Kenji Goto and troubled loner Haruna Yukawa, threatening to kill them if Tokyo did not pay Islamic State $200 million within 72 hours.

The Japanese government considers the deadline to be 2:50 p.m. local time (12.50 a.m. EST) on Friday.

"Kenji has always said he wanted to save the lives of children in war zones. He has reported on wars from an unbiased position. Kenji is not an enemy of the Islamic State. Please release him," Goto's mother, Junko Ishido, said in a statement released at a news conference.

"Japan has a war-renouncing clause in its constitution and has not fought a war for 70 years. Japan is not an enemy of Islamic countries and has kept ties of friendship," she said.

Prime Minister Shinzo Abe has said saving the men's lives is paramount but that Japan will not bow to terrorism.

Abe has ordered his government to make every effort to secure their safe release, setting off a flurry of activity among Japanese diplomats.

The captor in the video, which resembles those showing previous Islamic State captives, says the ransom demand matches the $200 million in aid that Abe pledged to help countries fighting Islamist militants.

Abe made the pledge during a multi-nation visit to the Middle East. Islamic State militants have seized large areas of Iraq and Syria, and beheaded several Western captives.

Japan stresses that its donation is for humanitarian aid, such as helping refugees, but insists it will not bow to terrorist threats.

Tokyo's most prominent mosque, the Tokyo Camii and Turkish Culture Center, posted a statement calling for the prompt release of the hostages.

It said Islamic State's actions are "totally against Islam and have a serious impact on Muslim communities all over the world and put Muslims in a precarious position".

Abe's handling of the hostage crisis - he must appear firm but not callous - will be a big test for the 60-year-old, but he appears to have few options. [ID:nL4N0V031R]

Yukawa, aged around 42 and who dreamed of becoming a military contractor, was captured in August outside the Syrian city of Aleppo. Goto, 47, a war correspondent with experience in Middle East hot spots, went to Syria in late October to try to help Yukawa.

"He left a very young baby and left his family and I asked his wife why he made this decision and she said he had to do everything in his power to save his friend and acquaintance and that it was very important to him," said Goto's mother, struggling to hold back tears.